CMP is a well known process in the semiconductor industry used to remove and planarize layers of material deposited on a semiconductor device to achieve a planar topography on the surface of the semiconductor device. To remove and planarize the layers of deposited material, CMP typically involves wetting a pad with a chemical slurry containing abrasive components and mechanically "rubbing" or "buffing" the front surface of a semiconductor device against the wet pad to remove the layers of deposited materials on the front surface of the semiconductor device and planarize the surface. The types of deposited materials removed and planarized may include metal layers as well as dielectric layers that form the front surface of the semiconductor device.
Typically, the CMP of a metal layer consists of two primary steps--a first step removes the metal layer on the front surface of the semiconductor device and planarizes the remaining surface; while a second "touch up" or "buff" step removes any contaminants remaining after the first step and re-planarizes the front surface. Each step requires the use of a chemical slurry as described above to remove the metal layer in the case of the first step and any remaining contaminants in the touch-up step. The chemical slurry used in each step may be composed of identical or different compositions depending on the CMP requirements.
Conventional CMP of metal layers also involves an intermediate rinsing step between the two primary steps described above. The intermediate rinsing step consists of repositioning the semiconductor device at a rinse station and spraying water at the front surface of the semiconductor device to remove the slurry from the first step prior to subjecting the device to the second slurry in the second step. It has been discovered by the Applicants that some of the chemical slurry from the first step remains "trapped" on the back surface of the semiconductor device that is not rinsed in the intermediate rinsing step since the water sprayed during this step only sprays the front surface and cannot reach the back surface of the semiconductor device.
A problem exists when the slurry used in the first step is not completely removed, prior to the second step, and mixes with the slurry used in the second step. Often, this mixing of the two slurries will cause a chemical reaction that results in particle generation that contaminates the semiconductor device and causes a severe effect on the yield and performance of such devices. A need therefore exists to remove the "trapped" slurry, on the back surface of the semiconductor device, to prevent particle generation caused by the mixing of the slurries after the primary steps. Any solution to this problem must significantly reduce particles and overall device defectivity, be performed at a low cost with few and simple additional process steps and be preferably ecologically safe with insignificant environmental impact.